Landing Page Feedback - Need Help Please

I would really appreciate it if someone can help me answer these questions:

  1. how do you make font-size responsive for different screen sizes? It was a mess, I had to adjust and re-adjust the sizing and it still isn’t great. I never know which units to use: em, rem, px, %? What’s best?
  2. my nav bar is a mess. I used grid with a flexbox <ul> within it. It looks ok on desktop, but I’m having such a hard time with the @media query for smaller screens. I can’ figure out how to wrap my <ul> onto a new line, so that my logo and name are on line 1 and <ul> items are on line two in the center.
  3. also I would really appreciate any other feedback. Despite having a general idea and understanding of flex, grid, and @media, when in the process I’m getting lost.
    Thanks a lot!
    Here is my code:
    https://codepen.io/nprymost/pen/ExLqQNZ

fyi: i made some edits to your post to make the html show up (you have to wrap it in backticks)